The cochlear implant is the first neural prosthesis to achieve the technical success necessary for widespread clinical application. It provides the only effective therapy for restoring sound sensation to the profoundly deaf. Over the past fifteen years dramatic advances in patients/ performance with these devices have been achieved (e.g., adults' average sentence recognition scores of 70-80% without speech reading). These advances have derived substantially from the collective efforts of researchers in a broad array of scientific disciplines. This close collaboration and cooperation has been fostered in large part through a series of biennial research conferences, originating with the 1983 Gordon Research Conference on Implantable Auditory Prosthesis. These conferences are the only forum in which implant research issues the sole focus. The theme of the 1997 conference was to understand factors underlying the wide variation of implantees' speech recognition scores. While those factors were addressed using a number of different approaches during that meeting, the issue of variability, the underlying reasons for that variability, and the appropriate treatment for patients with widely varying pathology are still important subjects for research and discussion. The focus of the 1999 conference will be in two general areas that we view as important follow-up to the last conference's discussions. The first area is a better understanding of the relationship between physiological and psychophysical measures. While physiological assessments provide the most direct measure of the auditory periphery, it is essential to place those measures in a context of behavioral performance. Psychophysical measures and their relationship to speech perception and speech processing will also be addressed. Understanding the link between mechanisms of neural excitation and the corresponding perception is essential to apply the knowledge gained from physiology to development of better speech processing strategies. The second area is the long-term effects of electrical stimulation. This topic will be approached through anatomical and physiological studies in addition to reports on developmental aspects in the use of cochlear implants. In each of these topics we will attempt to address further the important issues of individual differences, developing a better understanding of the basis of individual differences as well as the development of strategies for dealing with individual differences. This application seeks partial support for this conference.